The invention relates to a process for carrying out a release (i.e. a "validation") operation for a chip card with a user memory, in which the release (i.e. "validation") of a user function is made dependent on a preceding data comparison between externally entered data and reference data deposited in a code memory. The invention also relates to an apparatus for carrying out the process.
As is well known, integrated circuits with a non-volatile memory of the EPROM or E.sup.2 PROM type are placed on chip cards. In order to protect against abuse of the chip cards, they frequently contain a security logic which makes certain user functions such as readout, write, clear or comparison of the memory content dependent on the use of an internal chip data comparison between reference data which are deposited in a non-volatile manner in the memory and secret code data which must be entered by a user at a terminal. It is desired in many cases to make each use of this secret code recognizable for safety reasons so as to retain control over the memory access even in the case of a disclosure or misuse of the secret code. It is therefore possible to recognize unauthorized use and to limit the number of unauthorized attempts.
German Published, Non-Prosecuted Application DE-OS No. 33 15 047 discloses such an integrated circuit in which the clearing of an E.sup.2 PROM memory area remains in a non-volatile manner and is always recognizable in a counter with registers in a non-volatile manner.
Although the security for a chip card is considerably increased by these known measures, nevertheless not all abuses of the chip card can be prevented.
It is accordingly an object of the invention to provide a release process for an access-controlled user memory and for carrying out the process, which overcomes the hereinaforementioned disadvantages of the heretofore-known devices of this general type and to further improve the application of an integrated circuit of the type mentioned above.